As is widely known, an external gear shift control is the device usually used for the remote control of gear shifting in a vehicle when the gear box is located away from the control lever, and normally consists of an integrated set of mechanical elements which include a gear selector control lever, mechanical pivot elements, a support for these elements, and two push-pull type cables to transfer the selection and coupling motions from the lever to the gear motion system inside the gear box. A "push-pull" type transmission cable, which is a flexible element capable of transferring linear motion in both directions, is normally used for both the gear selection cable and the coupling cable. It consists of a specially manufactured flexible internal cable which enables traction and compression force to be transferred, and includes a flexible external casing or conduit in which the cable slides without play. The liner rigidity of the two elements along the cable axis determines the precision of motion transfer. Both ends of the internal cable have terminals which allow it to be connected pivotally to the motion transmission element and the receiving element, while the two ends of the external casing have fasteners to the gear shift command support and to the gear box, respectively.
Typically, the selection of gears is controlled by lateral movement of the lever, i.e., by motion across the direction of motion of the vehicle, and the gears are engaged by longitudinal motion of the lever, i.e., in the direction of motion of the vehicle. In order to accomplish the motion to control the gears, the lever pivots on the fixed base on the vehicle chassis by means of a pivot joint which allows it to pivot in all directions. This joint is frequently accomplished by means of a ball joint, consisting of a ball which pivots within a ball seat. Normally, the ball is a solid piece at the end of the lever, with the seat attached to the base. In cases in which the lower end of the lever pivots, the opposite arrangement is sometimes used, in which the ball is attached to the bottom of the base and the ball seat can move together with the lever. Different types of pivots are also used, such as a universal joint system, for example.
The longitudinal motion of the lever, which determines how the gears are engaged, is normally transferred directly to the terminal of the coupling cable, which is pivotally connected to the lever at a point determined by the functional characteristics of the gear system. When the motion of the coupling cable is to be in the same direction as the motion of the hand of the driver, the cable terminal must be connected to the lever at a point between the pivot joint and the hand of the driver. In the other case, when the system requires that the cable moves in a direction opposite to the direction of motion of the hand of the driver, the terminal connection must be below the pivot joint, usually at the lower end of the control lever. The distance along the lever axis between the pivot joint and the point of connection of the clutch cable terminal is in both cases equal to the lever arm necessary to provide travel to engage the gear in the gear box. Transverse motions of the lever, which determine which gear is selected, must be converted into longitudinal motions so that the two cables (selection and clutch) are parallel and thus extend to the gear box. In order to convert this motion, many different construction forms have been utilized. This motion is frequently converted by means of an L-shaped angular arm with 90 degree extension arms, the arms of which jointly pivot on a shaft, such that the angular arm receives the transverse motion of the lever at one of its ends and, by pivoting on an axis of rotation, transfers longitudinal motion to the cable terminal to which it is connected at the other end of the same arm, thus causing longitudinal motion in the cable which is proportional to the transverse motion of the lever. There are various possible configurations for operation of the angular lever arm.
The function of the support is essentially to form a rigid base for attaching the control lever pivot joint, the angular selection arm pivot shaft and the terminals of the outer casing of the coupling and selector cables, as well as for attaching the entire control device to the chassis of the vehicle. The external gear shift control is required to precisely transfer the gear selection and coupling motions to the gear box, and must be rigid enough to not transfer vibrations to the passenger compartment, must be light and compact enough to minimize weight and clearance, must be resistant to external agents and well protected from dust and other contaminants, and must facilitate maintenance and be economical in its construction so as to be competitive in the automotive industry.
In relation to these requirements, the control systems currently used have many disadvantages. In the rather common case of a control lever with a ball joint in which, for functional reasons, the coupling transmission cable must be activated by the lever at a position below the pivot, the construction of the lever with the ball and ball seat require laborious and lengthy machining, or else welding the lower part of the lever to the ball, requirements which do not facilitate the manufacturing process and jeopardize the strength of the system. The transverse motion of the lever is frequently transferred to an intermediate element which activates the selector cable by means of a ball which is attached laterally to the lever. Fastening this ball to the lever and the need to maintain the alignment with the center pivot point of the lever and the intermediate selection element, all complicate manufacturing and create installation and maintenance problems. Conversion of the transverse motion of the lever to the longitudinal motion of the selector cable also creates problems due the play of the intermediate components of the selection system. This play is most noticeable during motion, thus jeopardizing the precision of the gear shift. The play existing in the gear shift control also influences the transfer of noise from the engine and the transmission system through the cables. In various existing systems, the longitudinal or coupling motion of the lever causes some motion in the selection elements. This situation interferes to some extent with the selection control, making it difficult to change gears and increases the force required to operate the gear shift.